This invention relates to a system for locating the focal range of shockwaves generated by a shockwave source relative to a concrement situated in the body of a living being.
The ESWL (extracorporeal shockwave lithotrity) focal range may, particularly under anatomically unfavorable conditions, deviate considerably from the theoretical geometrically determined focus. Thus, exact positioning of the concrement to be treated is not possible in such cases, and the ESWL effectiveness is correspondingly low. Direct imaging of the shockwave propagation/focusing in the body cannot be carried out by means of the imaging methods known in the field of medicine.
In the apparatus disclosed in European Patent Document EP 367,116, the focal range is located indirectly by detecting motion in the body induced by the shockwaves. The ultrasonic Doppler process used in this device, however, measures only the radial speed with respect to the ultrasonic scanner from which the ultrasonic waves originate, and by which their echoes are received.
It is an object of the present invention to provide a system by means of which the focal range of the shockwave source can be reliably located, so that the concrement can be securely positioned in the focal range.
According to the invention, this object is achieved indirectly by detecting motion induced by the shockwaves, in the stone material, in the fluid surrounding the concrement or in the body tissue. (Another possibility is the movement of cavitation bubbles generated in the shockwave field.) Since such motion is most pronounced in the focal range, location of this region is possible.
The detection of induced motion in the interior of the patient's body takes place non-invasively by interpretation of an ultrasonic B-scan-image (also called simply a "B-scan-image") , used for the ESWL-locating of the stones. Such movements are detected by segmenting and correlating successive B-scan-images, in a device for the detection of the motion induced by the shockwaves. The comparison is not limited to images that follow one another directly (B.sub.i, B.sub.i+1), but advantageously, also permits comparison of images B.sub.i, B.sub.i+k, where k&gt;1. The determined speed values are used to generate a color-coded speed pattern, which may be superimposed on the ultrasonic B-scan-image.
In the case of such a speed pattern, a color/intensity combination is assigned to any combination of the amount/speed.
Imaging errors due to refraction and diffraction of sound inherent to the B-scan-image in this case do not have any effect on the location of the focal range, because the position of the focal range relative to the concrement is decisive for the ESWL-positioning.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.